A number of image capture systems, such as airborne or spaceborne camera or radar systems, diagrammatically illustrated at 10 and 11, respectively in FIG. 1, are employed to capture images of areas 12 of the surface of the earth. In a number of applications, these images are used to locate one or more features of interest, in preparation for further activity, such as, but not limited to tactical theatre-based interdiction of one or more targets whose geographical locations must not only be determined with high accuracy, but may vary over a relatively brief time interval (e.g., on the order of only several or tens of hours), making time of the essence.
Because the image capture platform is typically mounted on a reconnaissance aircraft 14 or the like, the parameters of an associated sensor geometry model 15, through which a captured digital image 16 may be related or transformed to the surface of (a digital elevation model (DEM) of) the earth containing the viewed area of interest, are not only affected by the orientation of the image capture device, but by the substantial dynamics (including avionics errors) of the aircraft itself. If uncompensated, these offsets will introduce errors in geographical coordinates of respective points (pixels) in the digital image that are obtained by mapping or `geolocating` respective pixels (some of which are shown at 17) of the digital image 16 to actual coordinates 21 (e.g., latitude-.PHI., longitude-.gamma. and elevation-h) on the surface of the earth.
To solve this problem, it has been customary practice to have a skilled operator at an image processing workstation 24 examine the display 25 of the `working` or input digital image 16 to locate what are known as `ground control points` 27. Such ground control points are those points whose actual geographical coordinates are known with a relatively high degree of accuracy (e.g., to within one to five meters, or less), such as may be obtained from a survey of the area of interest or from an archival `reference` image 29 of the geographical area of interest. By clicking on a display cursor 31 that has been manually positioned (mouse-manipulated) over a what is considered to be a respective ground control point in the working image, the operator supplies to an offset or error correction program within the workstation the apparent location of the pixel, which is then compared by the correction program with the actual coordinates of the known ground control point in the reference image 29. By repeating this operation for numerous ground control points, the operator sequentially supplies the image workstation's correction program with a relatively large number of data points, that the program uses to update or refine the parameters of the sensor geometry model associated with the working image, and thereby reduces what is originally a relatively large geolocation offset in pixels of the working image to one that is closer to the error resolution of the reference image.
A fundamental problem with this operator-controlled error reduction scheme is the fact that it is extremely labor intensive (and thereby subject to an additional source of error--the operator), and time consuming, often taking hours to complete. If the image is one containing features whose locations are not necessarily static and must be acted upon within a relatively short period of time of their identification, the conventional operator-controlled approach may have little or no practical value to the ultimate user of the working image. Moreover, the conventional approach requires a reference image that contains a sufficient number of valid ground control points whose accuracy has been predetermined, such as a `survey` map. If such ground control points have not been previously accurately located in such a reference image, it may not be possible for the operator to obtain any meaningful reduction in errors in the parameters used by the sensor geometry model for the working image.